His twin brother Juanmi is also a footballer, and both were Real Madrid graduates.[1] He began his career with its reserve clubs, but made a name for himself at Espanyol. In 2011 he returned to his previous team and, two years later, left for Napoli.

On 23 May 2011 Callejón rejoined Real Madrid on a five-year contract, effective as of 1 July, for a reported fee of €5.5 million.[8] On 16 July he played his first match for the Merengues, in a 4–1 friendly win with the Los Angeles Galaxy, scoring the first goal of the game in the 30th minute.[9]

On 2 October 2011 Callejón netted his first official goal for Real Madrid, after coming on midway through the second half of an away fixture against former club Espanyol: he scored from a Cristiano Ronaldoassist in an eventual 4–0 win, but did not celebrate the goal, instead raising his arms in the air in a mark of respect to his former employer.[10]

As a starter, Callejón continued with his impressive scoring form: on 17 December, he scored once in a 6–2 away win against Sevilla.[13] In the tie against SD Ponferradina for the season's Copa del Rey, he netted three of the Merengues' seven goals overall (one away, two at home).[14][15]

On 14 January 2012 Callejón scored the winner in a 2–1 success at Mallorca, helping the visitors come from behind with his 84th-minute long-range strike.[16] In the following matchday he added another, closing the score in a 4–1 home win over Athletic Bilbao.[17]

Callejón netted his first goal of 2014–15 on the opening day of the Serie A campaign, the opener in a 2–1 win over Genoa CFC.[25] His second came on 24 September, as he scored at the stroke of half-time to put Napoli up 3–2 against U.S. Città di Palermo in an eventual 3–3 home draw.[26] On 19 October he scored twice in a 2–2 draw at Internazionale, with all four goals coming in the last 11 minutes of the game.[27]

In the Derby del Sole match against A.S. Roma on 2 November, Callejón hit the post and had a shot saved off the line before eventually finding the net late on in Napoli's 2–0 victory.[28] The strike took his league goal tally to eight on the season, two more than his closest competitors, and he was included in the Serie A "Team of the Week."[29]